Enzymatic Modification And Functional Properties Of Rice Bran Dietary Fiber

The enzymatic modification was studied in this paper in view of the low content ofsoluble dietary fiber and poor functional properties of defatted rice bran dietaryfiber(DRBDF). The content of soluble dietary fiber was the important indicator of the qualityof dietary fiber. SDF was only1%2%in DRBDF, WHC was lower than that of corn andwheat bran dietary fiber, OHC was30%lower than that of wheat bran dietary fiber. Thus,enzymic modification was studied for DRBDF extracted from rice bran, aimed at improvingSDF content and functional properties.Thermostable α-amylase and Alcalase were used to remove starch and protein afterphytic acid decomposed. The purity of DRBDF was77.05%under the optimized condition ofα-amylase addition of200U/g, the hydrolysis time of30min and Alcalase addition of0.6%,the hydrolysis time of5h. Protein content of DRBDF was8.18%by the removal rate of60%,starch content was0.88%by the removal rate of96%. Infrared spectrum showed the typicalabsorption peaks of polysaccharides, SEM showed the lamellar structure. WHC, OHC, SC ofDRBDF were4.04g/g,2.56g/g,4.48mL/g respectively, cation exchange capacity was0.45mmol/g.The optimal conditions of hydrolyzation on DRBDF with cellulase and xylanase weregot from orthogonal experiments. In pH5.0, addition of65EGU cellulase per gram DRBDF,under the condition of50℃for3h, the SDF yield was up to6.97%. In pH4.5, addition of30FXU xylanase per gram DRBDF, under the condition of50℃for3h, the SDF yield was up to6.68%. WHC of C-IDF and X-IDF reached5.56,4.50g/g, increased by38%and11%respectively. OHC of C-IDF and X-IDF were5.49,5.20g/g,2.14times and2.03times that ofDRBDF respectively, SC reduced and CEC increased after enzymolysis.The physi-chemical properties of dietary fibers were studied. Infrared spectrum showedthe properties of polysaccharides in all fibers, phenolic characteristic absorption peak ofbenzene ring appeared in both X-SDF and C-SDF. Surface structures of X-SDF and C-SDFwere loose, C-IDF appeared more porous, many large cavities and cracks formed in X-IDF.The monosaccharides composition of the soluble fiber（X-SDF and C-SDF）were major inglucose, followed by xylose and arabinose, mannose was not determined in X-SDF.Glucose adsorption capacities of all the dietary fibers were significantly increased afterenzymatic hydrolysis. GDRI values in30min and60min of X-TDF and X-SDF were higherthan that of DRBDF, cellulase had no obvious effect on GDRI value in60min, but C-TDF,C-SDF could delay the glucose diffusion rate in vitro model. Adsorption of C-SDF andX-SDF for cholesterol at pH7were27.06,29.02mg/g, by30%and38.5%higher than that ofDRBDF respectively. Adsorption of X-IDF and C-IDF for cholesterol significantly decreased. C-TDF had the highest cholic acid sodium combining ability, followed by DRBDF, C-IDF,X-TDF, X-IDF, X-SDF, C-SDF. Viscosity and sodium cholate binding capacity of dietaryfiber were significantly (p<0.05) positive correlated, SDF and IDF were synergetic incombination for sodium cholate. NO2－scavenging capacity of almost all dietary fibers weresignificantly enhanced, however, scavenging capacity of C-IDF was nearly the same with thatof DRBDF.The in vitro antioxidant capacity study found that both cellulase and xylanase hydrolysiscould significantly increase the content of phenolics. Total phenol content of C-TDF andC-SDF were4.38and18.53mg gallic acid per gram sample,2.08and8.82times that ofDRBDF, TAC were2.13and4.86times that of DRBDF respectively. TPC and TAC of X-SDFwere4.50times and2.38times that of DRBDF. Scavenging capacity for DPPH·，HO·，O2－·of dietary fibers increased significantly after cellulase treatment. O2－·scavenging capacity,reducing power and total phenol content were positively related. The antioxidant activity ofall the dietary fibers were higher than that of0.5mg/mL VC in linoleic acid system, andshowed great resistance to lipid oxidation in high fat content cookies.